Interleukin 6 Function in the Skin and Isolated Keratinocytes Is Modulated by Hyperglycemia.

Diabetes currently affects over twenty-five million Americans. Annual health care cost of diabetes exceeds $254 billion and is associated with a distinct set of diabetic complications that include delayed wound healing and diabetic ulcers. Interleukin 6 (IL-6) plays an important role in wound healing and is known to be elevated in the serum of both type I and type II diabetes patients. This study assesses the expression and function of IL-6 in the hyperglycemic epidermis and keratinocyte culture. Streptozotocin-treated mice were wounded six weeks after induction of hyperglycemia. Wound closure, protein, and mRNA expression were assessed up to 13 days of postwounding. Wound closure was delayed 4-5 days in hyperglycemic animals. Hyperglycemic wounds displayed greater IL-6 and IL-6Rα protein expression at 1, 7, and 10 days of postwounding compared to euglycemic control. However, IL-6Rα mRNA expression was reduced at all time points beyond day 1, while IL-6 mRNA expression did not significantly differ at any time point. SOCS3 mRNA expression was higher in the hyperglycemic skin at every time point. Imaging of fluorescent immunohistology also revealed significantly lower expression of SOCS3, but higher nuclear pSTAT3 in the epidermis of the hyperglycemic skin. Primary mouse keratinocytes cultured in high glucose for 7 days displayed 2-fold higher IL-6Rα mRNA and higher rmIL-6-induced nuclear pSTAT3, but lower SOCS3 basal levels compared to normal glucose-cultured cells. Thus, it appears that delayed diabetic skin wound healing is associated with increased induction and expression of IL-6 and its receptor, but its function in epidermal keratinocytes may be impaired.

IL-6 deficiency exacerbates skin inflammation in a murine model of irritant dermatitis.

Contact dermatitis is the second most reported occupational injury associated with workers compensation. Inflammatory cytokines are closely involved with the development of dermatitis, and their modulation could exacerbate skin damage, thus contributing to increased irritancy. IL-6 is a pro-inflammatory cytokine paradoxically associated with both skin healing and inflammation. To determine what role this pleiotropic cytokine plays in chemically-induced irritant dermatitis, IL-6 deficient (KO), IL-6 over-expressing transgenic (TgIL6), and corresponding wild-type (WT) mice were exposed to acetone or the irritants JP-8 jet fuel or benzalkonium chloride (BKC) daily for 7 days. Histological analysis of exposed skin was performed, as was tissue mRNA and protein expression patterns of inflammatory cytokines via QPCR and multiplex ELISA. The results indicated that, following JP-8 exposure, IL-6KO mice had greatly increased skin IL-1ß, TNFα, CCL2, CCL3, and CXCL1 mRNA and corresponding product protein expression when compared to that of samples from WT counterparts and acetone-exposed control mice. BKC treatment induced the expression of all cytokines examined as compared to acetone, with CCL2 significantly higher in skin from IL-6KO mice. Histological analysis showed that IL-6KO mice displayed significantly more inflammatory cell infiltration as compared to WT and TgIL6 mice in response to jet fuel. Analysis of mRNA for the M2 macrophage marker CD206 indicated a 4-fold decrease in skin of IL-6KO mice treated with either irritant as compared to WT. Taken together, these observations suggest that IL-6 acts in an anti-inflammatory manner during irritant dermatitis, and these effects are dependent on the chemical nature of the irritant.

Estrogen suppresses heptatic IκB expression during short-term alcohol exposure.

OBJECTIVE: To assess the effects of sex steroids on hepatic inflammatory pathways in short-term chronically ethanol-fed rats. METHODS: Ovariectomized female Wistar rats (8-12 weeks old, n = 8 per treatment group) were implanted with osmotic pumps releasing 17ß-estradiol (20 µg/24 h) or testosterone (25 µg/24 h) and fed liquid diets with or without ethanol (8 % w/v) for two weeks. Hepatic expression of IκBα/ß, TNF-α, and IL-6 mRNA was examined by real-time PCR. Liver (nuclear) NFκB, IκBα and ß, IL-6, and IL-6Rα protein expression was examined by enzyme-linked immunosorbent assay (ELISA) or Western blot. RESULTS: Estrogen alone induced greater steatosis, NFκB translocation, TNF-α mRNA, as well as IL-6, and IL-6R protein. Alcohol consumption along with estrogen treatment further increased steatosis, NFκB translocation, TNF-α mRNA, and IL-6 protein. Conversely, neither estrogen nor ethanol consumption induced IκBα or IκBß mRNA or protein expression, while testosterone robustly induced these inhibitory proteins regardless of treatment. CONCLUSIONS: Estrogen exposure enhances alcohol-induced liver inflammation, and the anti-inflammatory effects of testosterone in the liver might be related to induction of IκB. Elevated inflammation in response to estrogen may overwhelm the regenerative influence of IL-6 in liver, leading to increased steatosis and greater liver damage.

IL-6 modulates alpha-smooth muscle actin expression in dermal fibroblasts from IL-6-deficient mice.

IL-6 deficient (IL-6KO) mice display significantly delayed cutaneous wound closure. Myofibroblasts are the primary mediators of wound closure, and alpha-smooth muscle actin (alpha-SMA) is a marker of fibroblast differentiation to the myofibroblast phenotype. Wounds from IL-6KO, and wild-type mice were collected up to 6 days following wounding. Expression of alpha-SMA mRNA was found to be increased in wounds of IL-6KO mice up to 48 hours post wounding, but decreased below wild-type levels by 72 hours. Recombinant IL-6 treatment of IL-6KO dermal fibroblasts showed an induction of alpha-SMA mRNA and protein peaking at 1 ng/ml cytokine, but declining at higher concentrations. Actinomycin-D treatment of fibroblast cultures indicated that recombinant mouse IL-6 (rmIL-6) induction of alpha-SMA mRNA appeared to be primarily transcriptionally regulated, and extracellular signal-regulated kinase 1/2 kinase, but not signal transducers and activators of transcription 3 was readily phosphorylated in rmIL-6 treated IL-6KO fibroblasts. A dose-response increase in the mRNA expression of the IL-6R signaling inhibitor protein suppressors of cytokine signaling (SOCS) 3 was also noted in rmIL-6-treated IL-6KO fibroblasts. These data indicate that alpha-SMA expression is dysregulated in IL-6KO mice. The expression of alpha-SMA induced by rmIL-6 in fibroblasts from IL-6KO mice appears to be transcriptionally modulated, dependent on JAK1 kinase, and possibly downregulated as a result of increased SOCS3 expression.

The ubiquitin-modifying enzyme A20 is required for termination of Toll-like receptor responses.

A20 is a cytoplasmic protein required for the termination of tumor necrosis factor (TNF)-induced signals. We show here that mice doubly deficient in either A20 and TNF or A20 and TNF receptor 1 developed spontaneous inflammation, indicating that A20 is also critical for the regulation of TNF-independent signals in vivo. A20 was required for the termination of Toll-like receptor-induced activity of the transcription factor NF-kappaB and proinflammatory gene expression in macrophages, and this function protected mice from endotoxic shock. A20 accomplished this biochemically by directly removing ubiquitin moieties from the signaling molecule TRAF6. The critical function of this deubiquitinating enzyme in the restriction of TLR signals emphasizes the importance of the regulation of ubiquitin conjugation in innate immune cells.